This invention relates to governors for mechanical timing mechanisms and more particularly to oscillating governors of the type with a ratchet bar having opposed ends which engage the teeth on a gear which is biased to rotate.
The security of handling cash in theft sensitive areas includes many physical protections. In many institutions, short term cash supplies are sealed in a drawer which opens only after a delay imposed by a timer. The interval is short enough that it offers no serious inconvenience, but it is longer than the time a thief is prepared to remain on the premises.
The M. H. Rhodes Co., a Connecticut manufacturer, has commercially marketed a timer for use on cash drawers. This particular timer has been unchanged for at least fifteen years. The product is commercially successful. However, the timer is prone to spontaneous failure, that is, it stops instantaneously and unpredictably, without bushing or pivot wear, and without significant contamination by foreign particles. The problem of stoppage is aggravated by the consequence that the cash which it protects becomes inaccessible until repairs can be made. The timer is often installed under a service contract. Under a service contract, an unreliable mechanism can cause unrecoverable costs. Installers particularly have a need for a more reliable mechanism.
The cause of the spontaneous stoppage lies in the governor. Every half cycle the ratchet bar must come to a full stop before it oscillates back in an opposite direction. This stoppage of the ratchet bar coincides with the maximum friction between the gear and an engaging tooth on the ratchet bar. Usually the angular force of the rotating gear is sufficient to overcome the momentary hiatus in ratchet bar motion; however, occasionally the ratchet bar locks against a gear tooth.
To correct the problem, the ratchet bar requires a means to store its dynamic energy when it temporarily stops before changing direction. It is an object of this invention to provide a means to store dynamic energy and thereby overcome the problem of erratic stoppage.
On Feb. 9, 1960, U.S. Pat. No. 2,924,102 issued to G. Drouhot. Droughot was concerned with the problem of "galloping" in a governor which resulted from excessive rotational bias on the toothed gear coupled with a shock or jolt to the mechanism. Drouhot proposed regulating the angular velocity of the rocker member by providing a reed member on the rocker, said reed member being inherently tuned to be mechanically resonant at a predetermined frequency or natural oscillation. One embodiment of Drouhot's invention included a V-shaped rocker having a reed projecting outwardly at the centre of the V. The reed is required to project substantially outwardly in order to counter-balance the weight of the V-shaped rocker about its centrally located pivot. This is necessary to balance the rocker and thereby minimize the effect of external shock
G. Drouhot did not address the problem of rocker stoppage, nor did he identify the solution of providing a reservoir to store the dynamic energy of the rocker in order to have that same energy available to overcome any momentary hiatus in movement of the rocker. Furthermore in his patent specification, the flexural oscillation of the reed occurs during the entire motion of the rocker.
The invention provides for a diming mechanism having governor for regulating the angular velocity of one toothed gear wheel in a plurality of intermeshing gear wheels, said governor having a ratchet bar with opposite ends; a rod projecting perpendicularly through the centre of gravity of the ratchet bar; a tooth on each opposite end of the ratchet bar, each tooth projecting generally in the same direction and perpendicular to the ratchet bar, said teeth adapted to engage the teeth on the one gear wheel biased to rotate about an axis parallel to the rod whereby said ratchet bar oscillates between a first position in which one tooth is engaged with the gear and a second position in which the other tooth is engaged with the one gear wheel said gear wheel advancing 1/2 tooth with each change in position of the ratchet bar; a spring having one end affixed to the ratchet bar; and an inertial mass affixed to the other end of the spring wherein said end of the spring being affixed to the inertial mass moves from an unloaded position just before the change in direction of oscillation, to a loaded position, and then back to the unloaded position just after the direction of oscillation has changed.
With the present invention, the spring and the inertial mass are inert for the greater part of the ratchet bar's travel. This is unlike the aforementioned use of the oscillating reed in the device of U.S. Pat. No. 2,924,102.